Cancer chemoprevention by dietary polyphenols

Cancer remains a major health problem and is one of the leading causes of deaths worldwide. Although cancer is a broad group of various diseases, all types of cancers are characterized by several common hallmarks that include: sustained proliferative signaling, evasion of growth suppression, resistance to cell death, enabling replicative immortality, induced angiogenesis, and accelerated invasion and metastasis. More recently, chronic inflammatory responses and epigenetic modulations have been recognized as shared characteristics among all cancer cells; in fact, it has become apparent that these two features play a major role in the causation and development of most human cancers. The transition from a healthy cell to a cancerous one is a process that usually takes many years and may be influenced by genetic factors. However, there is growing consensus that lifestyle and dietary factors might serve as a trigger for the initiation of a significant majority of sporadic, non-hereditary malignancies. Based upon laboratory science and epidemiological evidence, there is an indication that several nutritional compounds, either by themselves or a combination of several of them together, can help prevent the transition of a normal cell to develop into a premalignant one, or slow down the progression of a premalignant clone of cells from converting into a proliferative malignant mass. Accordingly, some of these naturally occurring nutritional compounds have been termed as “chemopreventive agents” or even “nutraceuticals.” Among this long list of chemopreventive nutritional compounds, dietary polyphenols have emerged as the frontrunners as potential anticancer agents. Among the most studied examples of these dietary polyphenols are epigallocatechin-3-gallate (EGCG) from green tea, genistein from soybean, resveratrol from grapes, and curcumin from turmeric. These compounds have been shown to exert a large spectrum of diverse different bioactivities that orchestrate in a dose- and cell typedependent manner. As discussed in this review, the anti-inflammatory as well as epigenetics-regulatory functions that could be attributed to these polyphenolic compounds might be primordial for their chemopreventive action